Method of electroforming on surfaces having projections

ABSTRACT

A method of electroforming on surfaces having relatively high projections by providing a shield of electrically non-conductive material to encircle a portion of the length of the projection and thereafter periodically raising the shield at a rate corresponding to the rate of deposition on the projections.

United States Patent Mattia June 20, 1972 [54] METHOD OF ELECTROFORMINGON SURFACES HAVING PROJECTIONS [72] Inventor: Michael Mattia, UpperDarby, Pa.

[ 73] Assignee: The Budd Company, Philadelphia, Pa.

[22] Filed: Dec. 7, I970 [21] Appl. No.: 95,548

[52] U.S. Cl. ..204/4, 204/23, 204/DIG. 7 [51] Int. Cl. ..C23b 7/00,C23b 5/00 [58] Field of Search ..204/D1G. 7, 9, 23, 4

[56] References Cited UNITED STATES PATENTS 2,115,616 4/l938 Brown..204/23 2.751.340 6/1956 Schaefer ..204/23 3,023,154 2/1962 Hough etal. ..204/242 FOREIGN PATENTS OR APPLICATIONS 904,572 1 H1945 France..204/242 OTHER PUBLICATIONS Racking Plating Fixtures for SpecialisedPurposes by J. C. Vaughan & I. A. Usher Metal Industry Sept. 14, 1945pgs. I70- 172.

Primary Examiner.lohn H. Mack Assistant Examiner-T. TufarielloAttorney-Thomas I. Davenport, Edward M. Farrell, John D. Sowell, AlfordL. Trueax, Jr. and William R. Nolte ABSTRACT A method of electrofomu'ngon surfaces having relatively high projections by providing a shield ofelectrically non-conductive material to encircle a portion of the lengthof the projection and thereafter periodically raising the shield at arate corresponding to the rate of deposition on the projections.

3 Clains, 5 Drawing Figures INVENTOR.

MICHAEL MATTIA 1AM (2.14M

AGENT P'A'TENTEflJunzo m2 saw 1 or 2 PRIOR ART METHOD OF ELECTROFORMINGON SURFACES HAVING PROJECTIONS Heretofore it has been found that whendepositing metal such as nickel on surfaces having relatively highprojections excessive build-up of deposited metal will occur on the freeend of the projections. This build-up alters the current flow in thebath material and thereby prevents the desired thickness of metaldeposit in areas adjacent the base of the projections. Varioustechniques have been tried to obtain the desired thickness of metal onthese surfaces, such as periodic reverse plating and thieving, but thesetechniques have been found to be unsuccessful.

Accordingly it is the principal object of this invention to provide animproved method of electrodepositing on a surface having relatively highprojections which avoids one or more of the disadvantages of prior artmethods.

It is still another important object of this invention to provide animproved method of uniformly electrodepositing on a surface havingrelatively high projections without producing low spots of insufficientthickness of deposit around the base of the projections.

In accordance with the invention a method of uniformly electrodepositingmetal on a surface having relatively high projections which methodcomprises providing a shield to encircle the projection along a portionof its length with said shield being spaced along said surface,electrodepositing the surface and said projection with the shield inplace, and thereafter moving said shield along the length of theprojection away from said surface at a rate commensurate with theelectrodeposition rate.

For a better understanding of the invention together with other andfurther objects thereof, reference is had to the following descriptiontaken in connection with the accompanying drawing.

In the drawing,

FIG. 1, prior art, is a perspective elevational view showing a part witha projection having a layer deposited thereon;

FIG. 2 is a sectional view taken along the lines 2-2 of FIG. 1 showingthe projection in section;

FIG. 3 is a perspective view of a part having a projection extendingupwardly therefrom;

FIG. 4 is a view partially schematic showing the part having a shieldabout the projection in the presence of a bath solution enablingdeposition on the part;

FIG. 5 is a sectional view taken along the lines 5-5 of FIG. 4 andshowing the shield around the projection in cross section.

Referring now to FIGS. I and 2 of the drawing there is shown a prior artarrangement in which a part having an upstanding projection II haselectrodeposited thereon a layer of metal 13 such as nickel. As seen inFIG. 2 the thickness of the deposited layer is non-uniform, being muchthinner at location A than at location B. Moreover the top of theprojection II develops a mushroom type head 15 which greatly interfereswith the laying down of a layer of uniform thickness adjacent the baseof the projection upon top surface 16 of the part 10.

In order to avoid the non-uniform build-up of layer thickness ofelectrodeposited material on a part, reference is now had to FIGS. 3 and4 wherein a part 21 having a projection 23 extending upwardly fromsurface 24 is provided. In accordance with the method of the presentinvention, a cylinder shield member 25 is supported over the projection23. The inside surfaces 26 of the wall of the cylindrical member isspaced concentrically from the external surfaces of the projection 23,while the bottom edge 28 of the cylindrical member is spaced from thesurface 24 of member 21. The cylindrical member 25 which is ofelectrically non-conductive material includes a top wall 29 which has asmall aperture 30 in line with the axis of the projection 23. The smallaperture allows air to escape as the cylindrical member is lowered intothe electro-forming bath 31 and also allows gas to escape duringelectrodeposition of the metal. The top wall of the cylinder furtherincludes an arm 33 mounted on a screw 34 so as to move axially with saldscrew. A plurality of electrically nonconductive upstanding plates 36,37, 38 and 39 engage the edge surfaces of plate member 21 to provideuniformity of deposition adjacent its edges, while plate member 40 ofelectrically non-conductive material is applied to the bottom face 39 ofthe plate member 21 to prevent deposition of metal on the under surfaceof the plate 21.

In the present instance the electrodeposition apparatus is shown ascomprising a tank 41 of electrically non-conductive material whichcontains the aforementioned electrolytic bath solution 31, which in thepresent instance may be a nickel sulfamate bath. Anodes 43 shownimmersed in the fluid ma be of depolarized nickel and connected to acurrent source such as a battery 45. The circuit may be a variableresistor 44 for varying the current through the bath. The part to beplated 21, shown in FIG. 5 may be of stainless steel and is in turnconnected to the negative pole of the battery.

In operation as the electrical circuit through the bath 31 is activated,deposition of metal occurs on the top surface 24 of part 21 as well asaround the external surface 47 of projection 23. However since thecylindrical shield 26 restricts the electron flow through solutioninteriorly of the cylinder 25, deposition occurs on the external surface47 of the projection 23 at a low rate and maintains the surface 47active. The presence of the shield 25 however precludes the build-up ofan enlarged mushroom type head 15 as seen in FIG. I. When the thicknessof the deposited layer on surfaces 24 and 47 reaches a predeterminedthickness, screw 34 may be turned a desired amount to raise sleeve 25 anextent to permit further deposition on the base portion of projection 23and on surface 24 adjacent the base of the projection. In this manner auniform build-up of material is applied to the projection as well as onsurface 24. Since the part 21 is of stainless steel, the same has apassive film hence the separation of the electrodeposited layer may bereadily accomplished.

While there has been described what at present is considered to be thepreferred embodiment of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention.

What is claimed is:

I. A method of coating a surface of an object having a main portion anda projecting portion extending therefrom, comprising the steps ofinserting said object in an electrodeposit bath solution, providing anelectrically non-conductive cylindrical member to surround saidprojecting portion along its length except for an area adjacent saidmain portion of said object, providing said cylindrical member with aclosure plate aligned with said projecting portion to restrict thecurrent path around said projecting portion to prevent excessivebuild-up of electrodeposited material along the length of the projectingportion surrounded by said member, and concentrating a plating operationat said area at which said projecting portion joins said main portion ofsaid object.

2. In the method of coating a surface of an object having a projectingportion as set forth in claim I including the step of providing saidclosure plate with an aperture aligned with the axis of said projectingportion to enable escape of gas during electrodeposition on saidprojecting portion.

3. In the method of coating a surface of an object having a projectingportion as set forth in claim 2 including the step of providing armmeans for supporting said cylindrical member, and the step of providingmeans to move said arm means and said cylindrical member along the axisof said cylindrical member.

2. In the method of coating a surface of an object having a projectingportion as set forth in claim 1 including the step of providing saidclosure plate with an aperture aligned with the axis of said projectingportion to enable escape of gas during electrodeposition on saidprojecting portion.
 3. In the method of coating a surface of an objecthaving a projecting portion as set forth in claim 2 including the stepof providing arm means for supporting said cylindrical member, and thestep of providing means to move said arm means and said cylindricalmember along the axis of said cylindrical member.